Airborne laser profiling of the arctic pack ice

Abstract Since 1964, airborne experiments over the Arctic pack ice have been conducted, on an opportunity basis, to test and evaluate the usefulness of various remote sensing systems for mapping and measuring sea ice conditions and features. This paper describes the results of an analysis of laser terrain profile data obtained with coincident photography from an altitude of 1000 ft over the sea ice fields of the Beaufort Sea in April 1968. Analysis of the data reveals that sea ice surface roughness and the nature of the roughness as well as relative surface reflectivities, which are both manifested in the laser terrain profile, can be used to interpret the categorical stages of ice development. The laser terrain profiler seemingly detected, with acceptable accuracy, all ice features traversed; however, ice pressure ridges, ice hummocks, or ice blocks could not be distinguished from each other on the record because the measurement is only two-dimensional. These features were always detectable even when occurring in rapid succession. Cracks are very discernible on the laser terrain profile record. Useful estimations of the thickness of sea ice from the laser data were not possible. The errors possible in interpolation of the aircraft altitude variations were unacceptable for determining the ice surface elevation above sea level. Five overflights were made over the drifting ice island WH-4. The profile data were adjusted for altitude error as well as possible, and corrected profiles were constructed. Estimates of the island elevations and thickness are presented. The average thickness was estimated at 79 ft and maximum thickness at 135 ft. The aircraft altitude errors were generally acceptable for these estimates since WH-4 was much thicker than sea ice, thus permitting thickness estimates less than 10% in error. This study indicates that laser records could be computer-analyzed for time-space frequency distributions of stages of sea ice development, ice pressure ridges, and water openings. Use of the laser altimeter data for modeling pressure ridges should be given detailed consideration in future experiments. Ground truth documentation will be necessary in future experiments to confirm the validity of laser height and slope measurements.